A growing concern among people in many countries is the spread of transgenes from transgenic crop plants to related wild species or nontransgenic plantings of the same crop. This fear is based in part on environmental concerns and also for unexpected potential side effects for human health. An important method for preventing unwanted hybridizing of transgenics will be to engineer genetic barriers that are not detrimental to the parent plants or to human consumers. This would require a simple genetic incompatibility. Wild populations are one important and largely untapped resource for identifying potential hybridization barriers that are not detrimental to parent strains. I propose here to map and identify two genes that cause temperature sensitive hybrid inviability of two Arabidopsis ecotypes. Once genes underlying the incompatibility of these strains have been identified, I will use transgenic and knockout approaches to elucidate the underlying molecular mechanism, and to test the whether we can elicit the inviability phenotype in hybrids of the transgenics. I will also analyze the population dynamics and molecular evolution of the incompatibility alleles to ask whether they have adaptive value to the parental strains. [unreadable] [unreadable]